1. Field of the Invention
The present invention relates to a liquid droplet jetting apparatus.
2. Description of the Related Art
In a liquid droplet jetting apparatus, such as an ink-jet printer, a pressure wave is generated by applying a voltage to a piezoelectric actuator, and a liquid such as an ink is made to be jetted from fine holes called nozzles. Therefore, a jetting performance is substantially affected by a variation and a change in a viscosity of ink.
It is possible to reduce a variation in a material and manufacturing by enhancing a production control, but at the time of use by a user, there occurs a variation and a change in the viscosity of ink due to a day-to-day change in temperature.
To cope with this change in the viscosity of ink, attempts have been made to detect a temperature around a recording head, and to keep constant a velocity of jetting of ink by changing a voltage to be applied to the piezoelectric actuator according to the temperature detected.
Even when the voltage to be applied is changed according to the temperature detected in such manner, since there is a variation in manufacturing of components of each recording head which cannot be ignored, various sorts of ranking of the voltage to be applied is necessary. Moreover, since a waveform control for jetting droplets of ink of various sizes is necessary, when the ranking of the voltage to be applied as described above is necessary in addition to the waveform control, checking of liquid droplet control in manufacturing of the recording head becomes extremely complex.
On the other hand, a head which is provided with a warm-up function to maintain the ink temperature to be not less than a certain fixed temperature all the time by heating the ink by providing a heater to the recording head has been known. However, this provision becomes expensive. Moreover, even when such heater is provided, it is difficult to provide such heater at a position where the heater makes a direct contact with the ink, and for increasing the temperature of ink, first of all, it is necessary to increase a temperature of a surrounding site, and it takes time for warming up.
Moreover, when a voltage is applied to a piezoelectric element, a deformation directly proportional to a strength of an electric field occurs (inverse piezoelectric effect), and causes heat generation by the piezoelectric element. Therefore, for heating the ink by using this, a method in which, a piezoelectric actuator (PZT) is driven prior to jetting of ink, and the temperature of ink is increased by the heat generation has been proposed (for example, refer to United States Patent Application Publication No. 2004/0135832 (corresponds to Japanese Patent Application Laid-open No. 2004-148784)).
In a liquid droplet jetting apparatus disclosed in United States Patent Application Publication No. 2004/0135832, since a pressure chamber is also deformed when the piezoelectric element is made to be deformed, when a voltage is let to be a drive voltage same as a voltage applied during a normal drive, ink droplets are jetted. Therefore, the drive voltage is controlled to be low at the time of increasing the ink temperature.
However, when the drive voltage is controlled to be low, an amount of deformation of the piezoelectric actuator is not much substantial, and a sufficient effect in heating the ink cannot be expected.